Human monocytes are critical cells in the initiation of the B cell activation process to antigens and certain mitogens. A very sensitive ELISA assay system has been developed which allows for the measurement of human B cell function in vitro. Elutriation technology will allow us to separate monocytes and evaluate the nature of their role in B cell activation. This system will also be utilized to localize the site(s) of BRM's activity in the cell-to-cell interactions operative in the human B cell activation process.